An oatp/LST gene group (SLC21 family) of organic anion transporters is a group of sodium-independent transporters known to play an important role plays an important role in homeostasis of the living body, such as incorporation of thyroid hormones via the blood-brain barrier into the central nerve system in the living body, transfer of bile acid or chemicals from blood to the liver, removal of inflammatory mediators such as pristanglandine or leukotriene, and excretion of foreign matters into bile or urine. For the oatp/LST group, there are reports on 13 types of transporters in human (for example, SLC21A3, SLC21A6, SLC21A11, SLC21A12 (Biochemical and Biophysical Research Communications, 273, 251, 2000) and 10 types of transporters in rat (for example, Slc21a1, Slc21a5 etc.), and depending on distribution of expression, the oatp/LST group is classified roughly into three types, i.e., transporters expressed specifically in the brain, expressed specifically in the liver, and expressed ubiquitously.
The organic anion transporters transport not only bile acid as substrate but also physiologically active substances such as thyroid hormones and conjugated steroids. Many of these substrates are ligands of intracellular receptors, and thus the organic anion transporters are considered to play an important role in initially taking the ligands of intracellular receptors into cells. However, the detailed mechanism is still not well elucidated. Accordingly, elucidation of the role of these transporters is considered to lead to development of therapeutic agents for various diseases.